Method system for control of gear selection in vehicles

ABSTRACT

A method of controlling gear selection in a vehicle transmission comprises detecting a change in a direction control signal (DCS) from a neutral signal state. If the current TOS is less than or equal to a predetermined neutral shift threshold TOS, the transmission selects one of a plurality of first direction gears if the DCS was changed to a first direction signal state or one of a plurality of second direction gears if the DCS was changed to a second direction signal state. If the current TOS is greater than the predetermined neutral shift threshold TOS, the transmission selects one of the plurality of first direction gears if a machine motion direction parameter indicates that the vehicle is moving in the first direction or one of the plurality of second direction gears if the machine motion direction parameter indicates that the vehicle is moving in the second direction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC § 119 and the ParisConvention to Inidan Patent Application No, 202011008117 filed on Feb.26, 2020.

TECHNICAL FIELD

The present disclosure relates to a method of controlling gear selectionin a transmission of a vehicle in response to a request by an operatorto shift the vehicle transmission out of neutral and to a control systemfor controlling gear selection when shifting out of neutral in vehicles.

BACKGROUND

Many vehicles, such as work machines, mining equipment and other workvehicles may include a powershift transmission coupled to a powersource, such as an internal combustion engine or an electric motor, inorder to provide more flexible use of the power output of the powersource. The transmission for such a vehicle typically comprises aplurality of speed and direction changing clutches, and a plurality oftransmission gears, wherein combinations of pairs of direction and speedchanging clutches effectively recruit transmission gears to provide aplurality of transmission gear ratios. The transmission may provide notonly a number of gears having gear ratios that enable the work machineto travel at a relatively wide range of speeds or conditions that mightbe impractical without a transmission, but also for a change of vehicledirection between forward and reverse. Some transmissions are configuredto change gears automatically in order to improve ease of operation ofthe vehicle through its speed range.

The direction of vehicle travel may be selectable by an operator via asuitable control device, such as a joystick. Operator selected directionshifts, to change the direction of travel while the vehicle is moving,are common especially with vehicles such as backhoe loaders andforklifts. Operators may also select a control setting for putting thetransmission in neutral during operation of the vehicle. This may occur,for example, during transition of the control device from a forwardposition to a reverse position of the control device through a neutralposition of the control device. Alternatively, an additional neutralizercontrol may be provided which overrides the position of the controldevice to put the transmission in neutral. With the transmission inneutral, the vehicle may speed up or slow down, for example whencoasting downhill.

When requesting a shift out of neutral, the Operator may request adirection matching or opposite to the current direction of motion of themachine. During a transmission shift, energy is transmitted to theclutch plates and the amount of energy is proportional to the speeddifferential of the clutch plates. In a high speed direction shift, theclutch plates are rotating in opposite directions with a high speeddifferential before engagement. Therefore, in the time it takes for theclutch to fully lock up, a large amount of energy may be transmitted tothe clutch plates, being converted from kinetic energy to heat energydue to friction. The increased energy requirement may cause increases inthe heat generated at the transmission clutches during the velocitychange, and can result in premature clutch failure when the clutchtemperature repeatedly exceeds the material durability limits of theclutch components. Similar issues can arise when the vehicle acceleratesor decelerates while in neutral and then a forward or reverse gear isengaged. Similar issues can also arise when the vehicle accelerates andclutches cause the vehicle to upshift and when the vehicle deceleratesand clutches maintain the current gear or downshift for engine braking.In some powershift transmissions, the incoming direction changing clutchis often most prone to damage as much of the energy of the vehicle iseffectively absorbed by the direction changing clutch.

There may also be a risk of over speeding of a power unit of the vehiclewhen engaging a gear on shifting out of neutral if the vehicle speed hasincreased while in neutral.

One option to mitigate this behaviour is to raise a warning, but thismay still allow the potential damage to occur. Another option when ahigh speed direction shift is requested is to inhibit a direction shift.Inhibiting a shift includes holding the original gear but limitingengine speed to slow the machine or selecting neutral to slow thevehicle. Inhibiting a shift may be problematic as the vehicle'sbehaviour may not be as the operator expects. Where the operator expectsa rapid deceleration, if only a moderate or no deceleration is realised,this may lead to degradation of control or the need to employinconvenient stopping mechanisms, such as dropping work tools oremploying the parking brake. Inhibiting a shift out of neutral may bedisadvantageous as it could lead to coasting, and unwanted increases inspeed. Inhibiting a shift may include holding the original gear orselecting neutral.

U.S. Pat. No. 9,689,490B2 describes a method for velocity change gearselection and shift execution for a motor grader, including a method forcontrolling directional shift gear selection. When the rotational speedof the transmission output shaft is greater than a predetermined limit,the transmission is prevented from shifting directly to a reverse gear.Instead, the transmission initially downshifts to a lower forward gear(e.g. from 4F to 3F) and a retarding force is applied to slow the workmachine until the rotational speed of the transmission output shaft isless than the predetermined maximum velocity limit. When the speed isless than the predetermined limit, the directional shift is completed byshifting the transmission to a lower reverse gear (e.g. from 3F to 1R).This is a combinational direction shift, i.e. there is a direction andgear number change. In some cases the direction shift is prohibiteduntil the operator slows the machine to below the predetermined speed.

There is a need for a control strategy to select an appropriate gearwhen shifting out of neutral and hence prevent the transmission damagewhilst maintaining vehicle control.

SUMMARY

The present disclosure therefore provides a method of controlling gearselection in a transmission of a vehicle, said vehicle having a powerunit and an automatic transmission, said transmission having a pluralityof first direction gears configured to move the vehicle in a firstdirection and a plurality of second direction gears configured to movethe vehicle in a second direction which is opposite to the firstdirection;

-   -   wherein a direction control signal is received from one or more        input devices controlled by an operator of the vehicle; and    -   a machine motion direction parameter is determined by a control        system of the vehicle;

the method comprising the steps of:

-   -   i) detecting a change in the direction control signal from a        neutral signal state to a first direction signal state or a        second direction signal state;    -   ii) determining a current transmission output speed;    -   iii) comparing the current transmission output speed with a        predetermined neutral shift threshold transmission output speed;        and either    -   iv a) if the current transmission output speed is less than or        equal to the predetermined neutral shift threshold transmission        output speed, causing the transmission to select a gear from the        plurality of first direction gears if the direction control        signal was changed to the first direction signal state or to        select a gear from the plurality of second direction gears if        the direction control signal was changed to the second direction        signal state; or    -   iv b) if the current transmission output speed is greater than        the predetermined neutral shift threshold transmission output        speed, causing the transmission to select a gear from the        plurality of first direction gears if the machine motion        direction parameter indicates that the vehicle is moving in the        first direction or to select a gear from the plurality of second        direction gears if the machine motion direction parameter        indicates that the vehicle is moving in the second direction.

The present disclosure also provides a control system for controllinggear selection in a transmission of a vehicle, said vehicle having apower unit and an indirect drive automatic transmission, saidtransmission having a plurality of first direction gears configured tomove the vehicle in a first direction and a plurality of seconddirection gears configured to move the vehicle in a second directionwhich is opposite to the first direction, said control system configuredto;

-   -   evaluate a direction control signal from one or more input        devices controlled by an operator of the vehicle; and    -   determine a machine motion direction parameter;    -   i) said control system being further configured to detect a        change in the direction control signal from a neutral signal        state to a first direction signal state or a second direction        signal state;    -   ii) determine a current transmission output speed;    -   iii) compare the current transmission output speed with a        predetermined neutral shift threshold transmission output speed;        and either    -   iv a) if the current transmission output speed is less than or        equal to the predetermined neutral shift threshold transmission        output speed, cause the transmission to select a gear from the        plurality of first direction gears if the direction control        signal was changed to the first direction signal state or to        select a gear from the plurality of second direction gears if        the direction control signal was changed to the second direction        signal state; or    -   iv b) if the current transmission output speed is greater than        the predetermined neutral shift threshold transmission output        speed, cause the transmission to select a gear from the        plurality of first direction gears if the machine motion        direction parameter indicates that the vehicle is moving in the        first direction or to select a gear from the plurality of second        direction gears if the machine motion direction parameter        indicates that the vehicle is moving in the second direction.

The present disclosure also provides vehicle comprising:

-   -   a power unit;    -   an indirect drive automatic transmission, said transmission        having a plurality of first direction gears configured to move        the vehicle in a first direction and a plurality of second        direction gears configured to move the vehicle in a second        direction which is opposite to the first direction;    -   an operator actuated input direction control configured to        generate direction control signals;    -   at least one transmission output speed sensor configured to        measure current speed of the transmission output and generate a        transmission output speed signal; and

the control system according to the present disclosure operativelyconnected to the power unit, transmission, input direction control, andat least one transmission output speed sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are described below, by way of exampleonly, with reference to the following drawings, in which:

FIG. 1 is a side elevation of a backhoe loader, being a vehicle suitablefor implementing the method and control system of the presentdisclosure;

FIG. 2 is a schematic diagram of a power train comprising a transmissioncontrol system for implementing the method of the present disclosure;

FIG. 3 is pictorial representation of a transmission system for thevehicle of FIG. 1 ;

FIG. 4 is a cross section representation of the transmission system ofFIG. 3 ;

FIG. 5 is a schematic diagram of a machine control system comprising thetransmission control system of FIG. 2 and associated control components;

FIG. 6 is a flow diagram illustrating a method according to the presentdisclosure;

FIG. 7 is a flow diagram illustrating a gear selection routine accordingto the method of the present disclosure;

FIG. 8 is a flow diagram illustrating a process for defining a machinemotion direction parameter according to the method of the presentdisclosure;

FIG. 9 is a flow diagram illustrating a further gear selection routineaccording to the method of the present disclosure;

FIG. 10 is a table of data for an exemplary directional shifting controllogic implemented by the transmission control system of FIG. 2 .

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a vehicle 10, in this case a backhoeloader, which is suitable to implement the method and control system ofthe present disclosure. The vehicle 10 may, however, be another type ofvehicle or work machine. The vehicle 10 may comprise a main unit 13having an operator cabin 14 for an operator and a power unit 19 (notshown in FIG. 1 ), such as an internal combustion engine, for providingpower to ground engaging means 15, such as tracks or wheels. The vehicle10 may comprise a first implement 11, in this example a bucket, and afirst arm arrangement 16 (a backhoe) to which the first implement 11 maybe connected via a known coupling arrangement 17. The vehicle 10 mayalso comprise a second implement 12, in this example also a bucket,attached to the main unit 13 via a second arm arrangement 18. The firstand second arm arrangements 16, 18 and the first and second implements11, 12 may be manoeuvred by means of a suitable hydraulic system as isknown in the art. Vehicles 10 suitable for implementing the method ofthe present disclosure may have any alternate configurations comprisingsome or no arms, implements and/or attachments depending on the intendeduse and function of the vehicle 10.

The ground engaging means 15 may be powered by an automatic transmission21 (see FIGS. 2 to 4 ) operatively connected between the power unit 19and the ground engaging means 15. A rotating power unit output shaft(not shown) may extend from the power unit 19 and may be connected to atransmission input shaft 22 directly, by a torque converter, or byanother indirect drive connection as is known in the art. Alternatively,the transmission 21 may be a direct drive system, which may require thesystem to be calibrated differently than for an indirect drive system. Atransmission output shaft 23 may be connected to the ground engagingmeans 15 by way of a final drive or the like (not shown). Thetransmission 21 may be a constant mesh transmission as illustrated, oranother type of transmission. As is known in the art, the transmission21 may comprise a series of gears that are selectively engaged by acombination of clutches 26 and brakes. The clutches 26 may comprise aplurality of speed changing clutches and direction changing clutches.Although not described in detail, combinations of direction and speedchanging clutches effectively provide a plurality of transmission gearswhich control the transmission of power between the power unit 19 andthe ground engaging means 15. The transmission gears may be provided tomove the vehicle 10 in a first (usually) forward direction and a second(usually reverse) direction. The transmission 21 may therefore have aplurality of first direction transmission gears, which may be forwardtransmission gears (for example 1F, 2F, 3F, 4F), and second directiontransmission gears, which may be reverse transmission gears (for example1R, 2R, 3R). A suitable shift control 20, such as a joystick or switcharrangement, may be provided in the operator cabin 14 to enable theoperator to select a desired direction of travel of the vehicle 10, i.e.forward, neutral or reverse, and thereby acts as an input directioncontrol 31. The input direction control 31 may further comprise aneutralizer control 20 a, for example a switch or trigger, may beprovided for selecting neutral without moving the shift control 20. Theneutralizer control 20 a may be provided on the shift control 20 or inany other suitable location. The shift control 20 may also enable theoperator to request a gear upshift or downshift, thereby acting as aninput gear control 32. The latter function may, however, be provided bya separate device, such as a switch. A suitable input speed control 30,such as a gas pedal or accelerator, may also be provided in the operatorcabin 14 to enable the operator to regulate the speed of the vehicle 10.The control device, including the shift control 20 and neutralizercontrol 20 a may generate a direction control signal to the transmissioncontrol system 24 indicative of the direction (forward, reverse orneutral), requested by the vehicle operator.

The transmission 21 may be electronically coupled to the transmissioncontrol system 24, which may electronically control operation of thetransmission 21 at least by controlling the engagement and disengagementof the clutches 26. The clutches 26 may be hydraulically actuatedclutches 26, which are disposed in a hydraulic circuit and are eachoperable to engage in a known manner in response to an actuating flow ofpressurised hydraulic fluid thereto. The transmission control system 24may comprise an on/off clutch control system which, during each gearshift, controls the requisite speed and direction clutches 26. Theclutches 26 may be controlled by means of a solenoid valve arrangementcomprising a solenoid corresponding to each clutch 26. Actuation of asolenoid, for example on receipt of a suitable control signal thereto,may cause the solenoid to direct an actuating flow of pressurisedhydraulic fluid to its respective clutch 26.

In the event of either a requested upshift or downshift in theforward/reverse direction, the on/off control mechanism effects theengagement of the oncoming speed clutch 26, by switching the associatedsolenoid on, and disengagement of the corresponding off going speedclutch 26, by switching the associated solenoid off. Where a directionshift is selected, the corresponding speed and direction clutch 26 isengaged and disengaged in a similar manner. Such on/off controlmechanisms are known in the art. Alternatively, the transmission systemmay have other types of clutch control, such as electronic clutchpressure control.

Although the physical configuration of the transmission control system24 is not illustrated, it may comprise a plurality of conventionalelectronic components, analogue-to-digital converters, input-outputdevices, solenoid drivers, electronic circuitry, and one or moreprocessors. It is to be understood that the one or more processors maycomprise one or more microprocessors, controllers, or any other suitablecomputing devices, resource, hardware, software, or embedded logic. Thetransmission control system 24 may comprise memory in the processors,main memory, and/or hard disk drives, which carry a set of non-transientmachine readable instructions or software/code which when executed bythe one or more processors, causes the transmission control system 24,to operate a gear selection routine 45, 145 in a manner as describedherein.

The transmission control system 24 may comprise a plurality ofcomponents or modules which correspond to the functional tasks to beperformed thereby. In this regard, “module” in the specification will beunderstood to include an identifiable portion of code, computational orexecutable instructions, data, or computational object to achieve aparticular function, operation, processing, or procedure. It followsthat a module need not be implemented in software; a module may beimplemented in software, optionally hardware, or a combination ofsoftware and hardware. Further, the modules need not necessarily beconsolidated into one system, but may be spread across a plurality ofother devices and systems to provide the functionality described herein.In one example embodiment, the one or more processors, executing theaforementioned machine readable instructions or software/code, mayeffectively provide the modules, or the functionality thereof, asdescribed herein.

As an alternative, the transmission control system 24 may be an analogor electromechanical device.

The transmission control system 24 may be part of the main machinecontrol system 25 (as shown in FIG. 5 ) which controls other functionsof the vehicle 10. The machine control system 25 may be of any suitableknown type and may comprise an engine control unit (ECU) or the like.The machine control system 25 may comprise a memory, which may storeinstructions or algorithms in the form of data, and a processing unit,which may be configured to perform operations based upon theinstructions. The memory may comprise any suitable computer-accessibleor non-transitory storage medium for storing computer programinstructions, such as RAM, SDRAM, DDR SDRAM, RDRAM, SRAM, ROM, magneticmedia, optical media and the like. The processing unit may comprise anysuitable processor capable of executing memory-stored instructions, suchas a microprocessor, uniprocessor, a multiprocessor and the like.Alternatively, the transmission control system 24 may be an independentcontrol unit connected electronically to the machine control system 25.

The machine control system 25 may be electronically connected to controlelements of the vehicle 10 as well as various input devices, forcommanding the operation of the vehicle 10 and monitoring itsperformance. The machine control system 25 may be connected to aplurality of input devices detecting operator input which provide demandsignals to the machine control system 25, that may include:—

-   -   the input speed control 30, which generates a speed control        signal;    -   the input direction control 31, which generates the direction        control signal; and    -   the input gear control 32, which generates a gear selection        signal.

The machine control system 25 may also be electronically connected to aplurality of sensing devices which provide sensor signals with valuesindicating real-time operating conditions of the vehicle 10. The sensorsmay include:—

-   -   at least one transmission output speed sensor 33 connected to        the output shaft 23, that transmits a transmission output speed        signal and may transmit values indicating the rotational        transmission output speed (TOS) of the transmission output shaft        23; and    -   an oil temperature sensor 36, such as a thermocouple disposed        within the transmission housing or other drivetrain component,        that may transmit an oil temperature sensor signal a value        corresponding to the oil temperature. Although the control        strategy described herein may not make use of oil temperature        values, temperature has a notable effect on transmission oil and        may prevent or allow certain modes of operation. Thus they may        be employed in a modified version of the strategy.

The machine control system 25 may also be electrically connected tooutput devices to which control signals are transmitted and from whichcontrol signals may be received by the machine control system 25. Theoutput devices may include:—

-   -   an engine throttle 37 that may control the speed of the power        unit 19;    -   one or more clutch actuators 38 that may control the        transmission clutches 26 (via the transmission control system        24) to switch between the available gears;    -   a brake actuator or actuators 39 that may cause hydraulic fluid        to flow to braking devices to engage and reduce the speed of the        vehicle 10; and    -   other retarding device actuators 40 that may be selectively        operated to reduce the TOS. Although the example of the control        strategy described herein may not make use of brake and        retarding systems, they may be employed in a modified strategy.

Referring to FIG. 6 and FIG. 7 , the transmission control system 24 maybe programmed to execute a gear selection routine 145 in response to arequest by the operator to shift out of neutral, via the input directioncontrol 31. The gear selection routine 145 may comprise a logic which isbased on a control strategy designed to prevent engine/transmissiondamage and assist operator control of the vehicle 10. The logic uses thecurrent TOS, as measured by the transmission output speed sensor 33, andcompares this with a predetermined neutral shift threshold TOSprogrammed into the transmission control system 24. The neutral shiftthreshold TOS may be the speed below which it is considered safe toallow the transmission to select drive out of neutral in the oppositedirection to the direction of travel such that damage is less likely tooccur. The logic matches the transmission gear direction to the machinemotion direction if the current TOS is over the neutral shift threshold,and matches the selected gear to the current TOS. The logic maytherefore inhibit a direction shift if the if the current TOS is overthe neutral shift threshold and the machine motion direction parameterdoes not indicate the same direction as the direction control signal.

The neutral shift threshold TOS for a vehicle 10 may be based on amaximum amount of energy that is expended to shift out of neutralwithout exceeding an operational limit of a component of the vehicle 10,such as the transmission 21 and the transmission clutches 26. Theneutral shift threshold TOS may be pre-programmed into the transmissioncontrol system 24. The neutral shift threshold TOS may be empiricallyderived from test data for the vehicle 10, and may be derived usingpower and energy analysis to determine the TOS limits which the clutches26 may take without incurring damage. Different configurations ofvehicles 10 and transmissions 21 may have different neutral shiftthreshold TOS's. The neutral shift threshold TOS may be a fixed value.For example, the neutral shift TOS threshold may be 1000 rpm. Theneutral shift threshold TOS for any vehicle may depend on any of anumber of parameters, including drive ratio, tyre size, vehicle mass andtransmission design.

FIG. 6 illustrates one embodiment of the control logic of the gearselection routine 145 for use in the vehicle 10 described hereinaccording to the method of the present disclosure. The gear selectionroutine 145 may begin at block 146, when a shift request is made by theoperator from neutral to forward or reverse.

If a request to shift out of neutral is determined, by a change in thedirection control signal from a neutral signal state to a forward orreverse signal state, control may pass to block 147.

At block 147 the transmission control system 24 may determine thecurrent TOS based on the measurements made by the transmission outputspeed sensor 33.

At block 148 the transmission control system 24 may compare the currentTOS with the neutral shift threshold TOS for the requested shift.

If the current TOS is equal to or less than the neutral shift thresholdTOS, control may pass to block 149, where a signal may be generated tothe transmission 21 which may cause it to select a gear from theplurality of forward direction gears if the direction control signal waschanged to the forward direction control signal state or to select agear from the plurality of reverse direction gears if the directioncontrol signal was changed to the reverse signal state.

If the current TOS is greater than the neutral shift threshold TOS,control may pass to block 150. At block 150, the gear selection routine145 may cause the transmission 21 to select a gear from the plurality offorward direction gears if a machine motion direction parameterindicates forward motion or to select a gear from the plurality ofreverse gears if the machine motion direction parameter indicatesreverse motion.

The machine motion direction parameter may be determined by thetransmission control system 24 according to a parameter setting methodas illustrated in FIG. 8 . When the current transmission output speed isbelow a direction detection threshold, the machine motion directionparameter is null. The direction detection threshold is a speed abovewhich it can be accurately determined that the machine is moving. Whenthe transmission output speed increases to or above a directiondetection threshold, the machine motion direction parameter is set tothe forward direction if a gear of the plurality of forward gears iscurrently engaged or to the reverse direction if a gear of the pluralityof reverse gears is currently engaged. The machine motion directionparameter remains fixed until the current transmission output speedpasses below the direction detection threshold. Therefore, the machinemotion direction parameter does not change directly from forward toreverse and changes only when the transmission output speed passes belowthe direction detection threshold value.

Alternatively, the machine motion direction parameter may be determinedby other suitable means, for example a direction detection sensorattached to the transmission output.

Each gear of the plurality of forward gears and the plurality of reversegears has a gear selection threshold transmission output speed. Inblocks 149 and 150, the specific gear selected from the plurality offorward gears or the plurality of reverse gears is selected bycomparison of the current transmission output speed with the gearselection threshold transmission output speeds.

A gear selection threshold TOS may be set for each gear, the gearselection threshold TOS representing a maximum TOS for shifting intothat particular gear. This threshold may be based on calculated orsensed speed which can be directly correlated to the power and energywhich the transmission must absorb or redirect. This threshold can bestored or calculated in real time.

The gear selected for a particular current TOS may be the lowest gearfor which the current TOS is less than or equal to the gear selectionthreshold TOS. If the current TOS is over the gear selection thresholdfor the highest gear in a particular direction, the highest gear in thatdirection may be selected.

As an example, the gear selection threshold TOS's may be as shown in thetable below.

Gear selection Gear threshold TOS (rpm) 1F (i.e. 1 Forward) 475 2F 12833F 1644 4F 3837 5F 3837 6F 3837 1R (i.e. 1 Reverse) 475 2R 1283 3R 1644

As a further example, the gear selection threshold TOS's may be as shownin the table below.

Gear selection Gear threshold TOS (rpm) 1F (i.e. 1 Forward) 475 2F 7523F 982 4F 1553 5F 2137 6F 5000 1R (i.e. 1 Reverse) 475 2R 752 3R 982

After the gear is selected in blocks 149 or 150, another gear selectionroutines or control methods may be used to determine subsequent gearchanges. For example, if the operator's selected direction differs fromthe actual machine direction, then a reduced engine speed may be used toslow the machine to a suitable speed before selecting the operators'requested direction. If the engaged direction matches the operator'srequested direction, then other gear shift routines may choose to modifythe gear and direction further in response to a change in vehicle speedor the operator's request.

Gear selection routine 145 may therefore form part of a gear controlmethod 155, which is illustrated in FIG. 7 . From blocks 149 or 150,control may pass to the start of gear control method 155.

As shown in FIG. 7 , the transmission control system 24 may continuouslyevaluate the value of the direction control signal from the inputdirection control 31. The gear selection routine 145 may therefore formpart of a continuously looping gear control method 155.

The gear control method 155 includes the steps (blocks 156 to 159) bywhich the direction control signal change from a neutral signal state toforward signal state or a reverse signal state is detected. As shown inFIG. 7 , the direction control signal may be in a neutral state ifeither a shift control 20 is in the neutral position or if a neutralizerswitch 20 a is activated by the operator. In gear control method 155,the transmission control system 24 detects if the shift control 20 is ina forward position or the reverse position in block 156. If the shiftcontrol 20 is not in the forward position or the reverse position (i.e.is in a neutral position), or if the neutralizer switch 20 a isdepressed, as checked in block 158, the transmission is placed inneutral (in a neutral condition), as shown at block 157, after which thegear control method loop 155 restarts.

At block 159, If the shift control 20 is in the forward position or thereverse position and the neutralizer switch is not depressed, thetransmission control system 24 compares the current direction controlsignal with that detected in the previous loop of method 155.

If the direction control signal was previously neutral, a directioncontrol signal change from neutral to forward or reverse has beenidentified, see block 146, and gear selection routine 145 may be carriedout as shown in FIG. 6 .

As shown in block 160, if the direction control signal in the previouscontrol loop was in the forward state or the reverse state (i.e. thedirection control signal was not neutral), the transmission controlsystem 24 may determine whether a direction shift from forward toreverse (or vice versa) has been requested. If a direction shift hasbeen requested, a further gear selection routine 45 (as shown in FIG. 9and described below) may be carried out. If a direction shift has notbeen requested (i.e. the direction control signal in the previous loopand the current loop of the routine is the same), the routine may returnto the start of method 155, detecting whether the shift control 20 is inforward or reverse.

References in this description to a position of a shift control 20 andneutralizer switch 20 a are given by way of example. The skilled personwill understand that the direction input control 31 may take anotherphysical form or may take a form other than device with differentphysical positions, for example touch screen controls, in which case the“positions” of the controls refer to different states of the control(e.g. a neutral state, a forward state and a reverse state) and“pressing the neutralizer switch” may comprise any form of activation ofa neutralizer control.

As shown in FIG. 9 , the transmission control system 24 may beprogrammed to execute a gear selection routine 45 in response to adirection shift requested by the operator via the input directioncontrol 31. The gear selection routine 45 may comprise a logic which isbased on a control strategy designed to prevent engine/transmissiondamage and assist operator control of the vehicle 10. The logic mayensure that the vehicle 10 is moving at an appropriate speed before adirection shift is executed. Thus the gear selection routine 45 mayinitially inhibit the requested direction shift. Where a requesteddirection shift is not executed immediately, the gear selection routine45 may be designed to execute one or more sequential downshifts from theinitial gear (i.e. the gear at the time the direction shift isrequested) to a secondary gear in the same direction of vehicle travelto assist in the deceleration of the vehicle 10. The gear selectionroutine 45 may also, under certain conditions, maintain the initial gearand may execute an engine speed reduction command which also assists inthe deceleration of the vehicle 10. The direction shift may then only beexecuted when the vehicle 10 is moving at the appropriate speed and theopposite direction gear selected may be that which matches the currentvehicle speed. Thus the same opposite direction gear may be selected asthe initial or secondary gear. The logic uses the current TOS, asmeasured by the transmission output speed sensor 33, and compares thiswith a predetermined direction shift threshold TOS programmed into thetransmission control system 24.

The direction shift threshold TOS for a vehicle 10 may be based on amaximum amount of energy that is expended to change the direction of thevehicle 10 without exceeding an operational limit of a component of thevehicle 10, such as the transmission 21 and the transmission clutches26. The direction shift threshold TOS may be pre-programmed into thetransmission control system 24. The direction shift threshold TOS may beempirically derived from test data for the vehicle 10, and may bederived using power and energy analysis to determine the direction shiftTOS limits which the clutches 26 may take without incurring damage.Different configurations of vehicles 10 and transmissions 21 may havedifferent direction shift threshold TOS's.

The machine control system 25 and/or the transmission control system 24may further be programmed with predetermined downshift inhibit thresholdTOS's for each downshift (i.e. to a same direction gear). These mayprevent the transmission 21 from downshifting to a lower gear that wouldrisk over speeding of the power unit 19.

FIG. 9 illustrates one embodiment of the control logic of a further gearselection routine 45 for use in the vehicle 10 described hereinaccording to the method of the present disclosure. The gear selectionroutine 45 may begin at block 46, when a direction shift request is madeby the operator from forward to reverse or vice versa. The transmissioncontrol system 24 may continuously evaluate the value of the directioncontrol signal from the input direction control 31 and will determinethat a direction shift request has been made when the direction controlsignal value changes from the current travel direction of the vehicle 10(the first direction) to the opposite direction (the second direction).If a direction shift request is determined, by a change in the directioncontrol signal, control may pass to block 47.

At block 47 the transmission control system 24 may determine the currentTOS based on the measurements made by the transmission output speedsensor 33.

At block 48 the transmission control system 24 may compare the currentTOS with the direction shift threshold TOS for the requested directionshift.

If the current TOS is equal to or less than the direction shiftthreshold TOS, control may pass to block 49, where the transmissiondirection shift signal may be generated to the transmission 21 which maycause it to execute the requested direction shift to same gear in thesecond direction (known as a straight directional shift). If there is nosame gear in the opposite direction (for example if there are 4 forwardgears and 3 reverse gears and the direction shift is from 4F) the shiftmay be made to the next highest gear in the other direction (in theforegoing example to 3R).

If the current TOS is greater than the direction shift threshold TOS,control may pass to block 50. At block 50, the gear selection routine 45may inhibit the direction shift and may generate one or moretransmission downshift signals to the transmission 21 to execute one ormore sequential downshifts to a lower gear in the first direction(hereinafter referred to as a secondary gear), or maintain the initialgear, until the current TOS drops to or below the direction shiftthreshold TOS. A change in gear due to the downshift may cause enginebraking to reduce the speed of the vehicle 10 and therefore the TOS. Thegear selection routine 45 may alternatively, or in addition, issue anengine speed reduction signal to reduce the engine speed (i.e. the speedof the power unit 19). The machine control system 25 may override theengine throttle 37 on receipt of such an engine speed reduction signal.Where the commanded engine speed is lower than the actual engine speed,the machine control system 25 may limit the supply of fuel to the powerunit 19, so that the power unit 19 may be turned by the transmission 21.This means that the transmission 21 may expend energy to turn the powerunit 19, which may reduce its speed. The engine speed reduction commandmay be limited so that there is no positive torque provided by the powerunit 19. Retardation may also be provided by pumping losses of the powerunit 19 and parasitic loads on the power unit 19 and the vehicle 10. Thelower gear (and torque converter characteristics) may act to back drivethe power unit 19 to the highest appropriate speed against these lossesto maximise the retardation effect. The gear selection routine 45 mayselect the lowest gear in the first direction which has a downshiftinhibit threshold TOS which is greater than the current TOS and maycause the transmission 21 to downshift sequentially to that gear. Thatgear may then be maintained until the current TOS drops to, or below,the direction shift threshold TOS.

If the initial gear has a downshift inhibit threshold TOS which isgreater than the current TOS, the gear selection routine 45 may maintainthe initial gear and wait for the current TOS to drop to or below thedirection shift threshold TOS generating the transmission directionshift signal.

Control may then pass to block 49 and, if the operator is stillrequesting the direction shift, i.e. the direction shift request isstill active, a transmission direction shift signal may be generated tothe transmission 21 which may cause a direction shift to be executed tothe same gear in the second direction (or the next highest in the eventof there being no corresponding gear in the second direction).

In any aspect of the present disclosure, the neutral shift threshold,which is the threshold applied when shifting out of neutral, may be thesame as the predetermined direction shift threshold. Alternatively, theneutral shift threshold and the predetermined direction shift thresholdmay be different values.

INDUSTRIAL APPLICABILITY

The method of the present disclosure which executes gear selectionroutine 145 and gear selection method 155 is particularly suitable for avehicle which uses an on/off clutch control system such as a back hoeloader, although it can be applied to other types of vehicles operatingother types of clutch control. The methods of the present disclosure maybe effective in limiting transmission damage when shifting into gear outof neutral. The logic used in these methods may inhibit a requesteddirection change when the transmission output speed is too high and maytherefore mitigate degradation and premature failure of the transmissionclutches.

According to the present disclosure, a method of controlling gearselection in a vehicle transmission comprises detecting a change in adirection control signal (DCS) from a neutral signal state. If thecurrent TOS is less than or equal to a predetermined neutral shiftthreshold TOS, the transmission selects one of a plurality of firstdirection gears if the DCS was changed to a first direction signal stateor one of a plurality of second direction gears if the DCS was changedto a second direction signal state. If the current TOS is greater thanthe predetermined neutral shift threshold TOS, the transmission selectsone of the plurality of first direction gears if a machine motiondirection parameter indicates that the vehicle is moving in the firstdirection or one of the plurality of second direction gears if themachine motion direction parameter indicates that the vehicle is movingin the second direction.

The following provides examples of gear selection routine 145 and gearselection method 155 according the present disclosure. In the followingexamples, the neutral shift transmission output speed threshold may be1000 rpm. These examples are provided to assist in understanding of themethod and control system of the present disclosure and are not to beconsidered limiting.

In a first example, the machine may be travelling downhill with atransmission output speed of 1800 rpm in the forward direction (suchthat the machine motion direction parameter is forward) when theoperator requests a directional shift, changing the direction controlsignal from forward, to neutral (momentarily) and then to reverse.

Initially, prior to the request for the directional shift, starting frombox 156 of the gear control method, the direction control signal remainsin the forward state. The control sequence passes through box 158 (asthe neutralizer switch is not pressed) to box 159. As the directioncontrol signal in the previous loop was in the forward state, controlpasses to box 160, beginning gear selection routine 45. At this point,as a direction shift has not yet been requested, the routine returns tothe start of method 155 detecting the position of the shift control 20.

When the shift control 20 is moved momentarily to neutral, the directioncontrol signal changes to the neutral state, and the control system maycause the transmission to be placed in neutral. The routine then returnsto the start of method 155, detecting the position of the shift control20.

When the shift control 20 is moved to reverse, on detecting the positionof the shift control 20, the control sequence passes through box 158 tobox 159 (because the neutralizer switch is not pressed). As thedirection control signal in the previous loop was in the neutral state,a request to shift out of neutral is detected and control passes to box146, beginning gear selection routine 145.

In this example the current transmission output speed remains over theneutral shift threshold value (1800 rpm vs 1000 rpm). Therefore, thetransmission control system 24 selects a forward gear in accordance withthe machine motion direction parameter as in box 150. The forward gearselected (e.g. 2F, 3F, 4F) may be matched to a current transmissionoutput speed. The routine may then return to the start of method 155,detecting the position of the shift control 20.

The method then continues through blocks 156, 158 and 159 (in thatorder). The direction control signal in the previous control loop wasnot neutral, and so the sequence passes to block 160. At this stage, theoperator is requesting the reverse direction via the shift control 20and the machine is moving forwards with the transmission in a forwardgear. Therefore, the transmission control system 24 determines that adirection shift request has been made by the vehicle operator to movethe vehicle from the forward to the reverse direction when thetransmission is in an initial forward direction gear and applies routine45. If the current transmission output speed remains over thepredetermined direction shift threshold, the control system may slowdown the machine, downshift the gears and reduce the transmission outputspeed, shifting to reverse when the transmission output speed is lessthan or equal to the predetermined direction shift threshold if operatoris still requesting the direction shift.

In an addition to the first example, if the operator of the vehiclepresses and releases the neutralizer switch after moving the shiftcontrol 20 to reverse, the control system may detect a further changeout of neutral. Assuming that the transmission output speed remains overthe threshold, the control routine may pass again to box 149 and mayfollow the remaining routine as described in the first example above.

In a second example, the machine may be travelling on a flat road with atransmission output speed of 1800 rpm in the forward direction (suchthat the machine motion direction parameter is forward) when theoperator presses and releases the neutralizer switch 20 a.

Initially, prior to the pressing of the neutralizer switch 20 a andstarting from box 156 of the gear control method, the direction controlsignal remains in the forward state. The control sequence passes throughbox 158 to box 159 (because the neutralizer switch is not pressed). Asthe direction control signal in the previous loop was in the forwardstate, control passes to box 160, beginning gear selection routine 45.At this point, as a direction shift has not been requested, the routinemay return to the start of method 155, detecting the position of theshift control 20.

When the neutralizer switch 20 a is pressed by the operator, thedirection control signal may change to the neutral state, and thetransmission control system 24 may cause the transmission to be placedin neutral. The routine may then return to the start of method 155,detecting the position of the shift control 20.

When the neutralizer switch 20 a is released, on detecting the positionof the shift control 20, the control sequence passes through box 158 (asthe neutralizer switch is not pressed) to box 159. As the directioncontrol signal in the previous loop was in the neutral state, a requestto shift out of neutral is detected and control passes to box 146,beginning gear selection routine 145.

In this example the current transmission output speed remains over theneutral shift threshold value (1800 rpm vs 1000 rpm). Therefore, thetransmission control system 24 may select a forward gear in accordancewith the machine motion direction parameter as in box 150. The forwardgear selected (e.g. 2F, 3F, 4F) may be matched to the currenttransmission output speed. The machine therefore continues forwards inan appropriate gear for the current transmission output speed. Theroutine then returns to the start of method 155.

In a third example, the machine may be travelling downhill with atransmission output speed of 700 rpm in the forward direction (such thatthe machine motion direction parameter is forward) when the operatorrequests a directional shift, changing the direction control signal fromforward, to neutral (momentarily) and then to reverse.

Initially, prior to the request for the directional shift, starting frombox 156 of the gear control method, the direction control signal remainsin the forward state. The control sequence passes through box 158 to box159 (because the neutralizer switch is not pressed). As the directioncontrol signal in the previous loop was in the forward state, controlpasses to box 160, beginning gear selection routine 45. At this point,as a direction shift has not been requested, the routine returns to thestart of method 155, detecting the position of the shift control 20.

When the shift control 20 is moved momentarily to neutral, the directioncontrol signal changes to the neutral state, and the control system maycause the transmission to be placed in neutral. The routine then returnsto the start of method 155, detecting the position of the shift control20.

When the shift control 20 is moved to reverse, on detecting the positionof the shift control 20, the control sequence passes through box 158 tobox 159 (because the neutralizer switch is not pressed). As thedirection control signal in the previous loop was in the neutral state,a request to shift out of neutral is detected and control passes to box146, beginning gear selection routine 145.

In this example the current transmission output speed remains under theneutral shift threshold value (700 rpm vs 1000 rpm). Therefore, thetransmission control system 24 selects a reverse gear in accordance withthe direction control signal as in box 149. The reverse gear selected(e.g. 2R, 3R, 4R) may be matched to the current transmission outputspeed. The machine therefore switches into reverse gear as requested bythe operator.

The routine then returns to the start of method 155, detecting theposition of the shift control 20.

In a fourth example, the machine may be travelling on a flat road with atransmission output speed of 700 rpm in the forward direction (such thatthe machine motion direction parameter is forward) when the operatorpresses the neutralizer switch, slows the machine further and releasesthe neutralizer switch.

Initially, prior to the request for the directional shift, starting frombox 156 of the gear control method 155, the direction control signalremains in the forward state. The control sequence passes through box158 to box 159 (because the neutralizer switch is not pressed). As thedirection control signal in the previous loop was in the forward state,control passes to box 160, beginning gear selection routine 45. At thispoint, as a direction shift has not been requested, the routine returnsto the start of method 155, detecting the position of the shift control20.

When the neutralizer switch 20 a is pressed by the operator, thedirection control signal may change to the neutral state, and thecontrol system may cause the transmission to be placed in neutral. Theroutine may then return to the start of method 155, detecting theposition of the shift control 20.

When the neutralizer switch 20 a is released, on detecting the positionof the shift control 20, the control sequence passes through box 158 tobox 159 (because the neutralizer switch 20 a is not pressed). As thedirection control signal in the previous loop was in the neutral state,a request to shift out of neutral is detected and control passes to box146, beginning gear selection routine 145.

As the current transmission output speed remains under the neutral shiftthreshold value, the control system selects a forward gear in accordancewith the direction control signal as in box 149. The forward gearselected (e.g. 2F, 3F, 4F) may be matched to the current transmissionoutput speed. The machine therefore continues forwards in an appropriategear for the current transmission output speed. The gear selectionroutine 145 then returns to the start of method 155.

The method of the present disclosure which executes the gear selectionroutine 45 is also particularly suitable for a vehicle which uses anon/off clutch control system such as a back hoe loader, although it canbe applied to other types of vehicles operating other types of clutchcontrol. This method may be effective in limiting transmission damage asa result of heat energy dissipation to the clutches from high speeddirectional shifts and may therefore mitigate degradation and prematurefailure of the transmission clutches. The logic used in the gearselection routine 45 may control the TOS by means of downward shifts inthe same direction to slow the vehicle 10 to a speed where a straightdirection shift to reverse the direction of travel may not causetransmission damage. The method does not attempt to impose any timeconstraint on the direction shift, only on the speed. Time based controlstrategies may suffer from a lack of feedback from the system. By usingspeed, the strategy may respond faster or slower, depending on thesystem and may provide better performance and protection.

Examples of the logic steps performed in the gear selection routine 45as executed by the transmission control system 24 are given in the tableof FIG. 10 . This will now be described in more detail based on anexemplary transmission 21 having four forward transmission gears 1F, 2F,3F, 4F and three reverse transmission gears 1R, 2R, 3R and a directionshift threshold TOS of 1000 rpm. The downshift inhibit threshold TOS'sfor this example may be as shown in the table below.

Downshift inhibit Downshift threshold TOS 4F-3F 1345 3F-2F 1020 2F-1F717 2R-1R 717 3R-2R 1345

It should be noted that the table shown in FIG. 10 does not refer to 1For 1R as an initial gear for a direction shift. This may be because, inthis embodiment, the current TOS may not reach a damaging speed in thesegears. Furthermore 1F or 1R may be avoided in the downshift strategy ofthe gear selection routine 45 to prevent too much torque passing throughthe transmission, which may be more torque than expected by theoperator. Alternatively the vehicle 10 may be travelling too fast, whichmay cause damage to 1R/1F if the gear was suddenly reduced. This may bea separate control strategy to prevent the power unit 19 from overspeeding.

The control strategies of the present disclosure may be designed tointeract with other control strategies which the transmission controlsystem 24 and/or machine control system 25 are programmed to implement.

If the initial gear (i.e. the gear when the direction shift isrequested) is 3F and the current TOS is equal to or below the directionshift threshold TOS of 1000 rpm, the gear selection routine 45 maygenerate a transmission direction shift signal which causes thetransmission 21 to immediately execute the direction shift to 3R (i.e.the direction shift is executed to the same gear in the otherdirection). However, if the current TOS is over 1000 rpm, say 1010 rpm,the gear selection routine 45 may initially inhibit the direction shift(by not generating a generate a transmission direction shift signal) andmay generate a transmission downshift signal to cause the transmission21 to execute a downshift to the next lowest gear 2F in the samedirection (i.e. a secondary gear). The gear selection routine 45 mayalso generate an engine speed reduction signal to reduce the enginespeed. A reduction in engine speed and/or a lower gear may retard thespeed of the vehicle 10 and reduce the current TOS. Unfavourable grades,payloads, frictional effects, lack of engine power may be variableswhich also help the vehicle 10 to slow naturally. When the current TOSfalls to or below 1000 rpm, and the operator is still requesting adirection shift, the gear selection routine 45 may generate atransmission direction shift signal to cause the transmission 21 toexecute the direction shift to 2R (i.e. the direction shift is executedto the same gear in the second direction).

The gear selection routine 45 may not select 1F as a secondary gear fora further downshift, as the downshift inhibit threshold TOS for a 2F-1Fdownshift in this example is 717 rpm, which is below the direction shiftthreshold TOS of 1000 rpm for a 2F-2R direction shift. The same appliesin reverse (i.e. selecting 1R). This may apply to each of the followingexamples.

If the initial gear is 2F and the current TOS is equal to or below thedirection shift threshold TOS of 1000 rpm, the gear selection routine 45may generate a transmission direction shift signal which immediatelycauses the transmission 21 to execute a direction shift to 2R (i.e. thedirection shift is executed to the same gear in the second direction).However, if the current TOS is over the 1000 rpm, the gear selectionroutine 45 may initially inhibit the direction change by maintaining theinitial gear 2F generate an engine speed reduction signal to reduce theengine speed. When the current TOS falls to or below 1000 rpm, the gearselection routine 45 may generate a transmission direction shift signalwhich causes the transmission 21 to execute the direction shift to 2R(i.e. the direction shift is executed to the same gear in the seconddirection).

If the initial gear is 4F and the current TOS is equal to or below thedirection shift threshold TOS of 1000 rpm, the gear selection routine 45may generate a transmission direction shift signal to cause thetransmission 21 to immediately execute the direction shift to 3R (i.e.the next highest reverse gear as there is no 4R in this example).However, if the current TOS is over 1000 rpm, for example at 1010 rpm,the gear selection routine 45 may initially inhibit the direction shiftand may generate a transmission direction shift signal to cause thetransmission 21 to execute a first downshift 3F as a first secondarygear in the same direction, then a second downshift to 2F as a secondsecondary gear. The gear selection routine 45 may also generate anengine speed reduction signal to reduce the engine speed. When thecurrent TOS subsequently falls to or below 1000 rpm, the gear selectionroutine 45 may generate a transmission direction shift signal to causethe transmission 21 to execute the direction shift to 2R (i.e. thedirection shift is executed to the same gear in the second direction).

If the direction shift is requested when the initial gear is 4F and thecurrent TOS, for example 1050 rpm, only a first downshift from 4F-3F maybe performed as the current TOS is higher than the downshift thresholdTOS for a 3F-2F (i.e. 1020 rpm). 3F may therefore be the secondary gearwhich will remain selected until the current TOS subsequently falls toor below 1000 rpm, at which point the gear selection routine 45 maygenerate a transmission direction shift signal to cause the transmission21 to execute the direction shift to 3R (i.e. the direction shift isexecuted to the same gear in the other direction). In this case, 2F mayor may not be selected when the current TOS is between 1000 rpm and 1020rpm, depending on calibration.

If the initial gear is 3R and the current TOS is equal to or below thedirection shift threshold TOS of 1000 rpm, the gear selection routine 45may generate a transmission direction shift signal to cause thetransmission 21 to execute the direction shift to 3F (i.e. the directionshift is executed to the same gear in the other direction). However, ifthe current TOS is over 1000 rpm, for example at 1010 rpm, the gearselection routine 45 may initially inhibit the direction shift and maygenerate a transmission direction shift signal to cause the transmission21 to execute a downshift to 2R, which is the secondary gear in the samedirection. The gear selection routine 45 may also cause generate anengine speed reduction signal to reduce the engine speed. When thecurrent TOS falls to or below 1000 rpm, the gear selection routine 45may generate a transmission direction shift signal to cause thetransmission 21 to execute the direction shift to 2F (i.e. the directionshift is executed to the same gear in the second direction).

If the initial gear is 2R and the current TOS is equal to or below thedirection shift threshold TOS of 1000 rpm, the gear selection routine 45may generate a transmission direction shift signal to cause thetransmission 21 to execute the direction shift to 2F (i.e. the directionshift is executed to the same gear in the other direction). However, ifthe current TOS is over 1000 rpm, the gear selection routine 45 mayinitially inhibit the direction shift and maintain the initial gear 2Rand generate and engine speed reduction signal to reduce the enginespeed. When the current TOS falls to or below 1000 rpm, the transmissioncontrol system 24 may generate a transmission direction shift signal tocause the transmission 21 to execute the direction shift to 2F (i.e. thedirection shift is executed to the same gear in the second direction).

In any aspect of the disclosure, the “current TOS” in a subsequentcontrol loop or method may be an updated current TOS for that loop ormethod. Similarly, the direction control signal in a subsequent controlloop or method may be an updated direction control signal for that loopor method.

In any aspect of the disclosure, the first direction may be one of aforward or reverse direction and a second direction may be the other ofthe forward or reverse direction.

The invention claimed is:
 1. A method of controlling gear selection in atransmission of a vehicle, said vehicle having a power unit and anautomatic transmission, said transmission having a plurality of firstdirection gears configured to move the vehicle in a first direction anda plurality of second direction gears configured to move the vehicle ina second direction which is opposite to the first direction; wherein adirection control signal is received from one or more input devicescontrolled by an operator of the vehicle; and a control system of thevehicle determines a machine motion direction parameter according to aparameter setting method, in which: when the transmission output speedis below a direction detection threshold, the machine motion directionparameter is set to null; and when the transmission output speedincreases to or above the direction detection threshold, the machinemotion direction parameter corresponds to the first direction if a gearof the plurality of first direction gears is currently engaged or to thesecond direction if a gear of the plurality of second direction gears iscurrently engaged; and wherein the machine motion direction parameterremains fixed until the transmission output speed passes below thedirection detection threshold; the method comprising the steps of: i)detecting a change in the direction control signal from a neutral signalstate to a first direction signal state or a second direction signalstate; ii) determining a current transmission output speed; iii)comparing the current transmission output speed with a predeterminedneutral shift threshold transmission output speed; and either iv a) ifthe current transmission output speed is less than or equal to thepredetermined neutral shift threshold transmission output speed, causingthe transmission to select a gear from the plurality of first directiongears if the direction control signal was changed to the first directionsignal state or to select a gear from the plurality of second directiongears if the direction control signal was changed to the seconddirection signal state or iv b) if the current transmission output speedis greater than the predetermined neutral shift threshold transmissionoutput speed, causing the transmission to select a gear from theplurality of first direction gears if the machine motion directionparameter indicates that the vehicle is moving in the first direction orto select a gear from the plurality of second direction gears if themachine motion direction parameter indicates that the vehicle is movingin the second direction.
 2. A method as claimed in claim 1 wherein eachgear of the plurality of first direction gears and the plurality ofsecond direction gears has a gear selection threshold transmissionoutput speed; and wherein the gear selected from the plurality of firstdirection gears or the plurality of second direction gears is selectedby comparison of the current transmission output speed with the gearselection threshold transmission output speeds.
 3. A method as claimedin claim 1 comprising detecting an updated direction control signalafter step iv a) or iv b) and either: if the updated direction controlsignal is in the neutral signal state, placing the transmission in aneutral condition; or if the updated direction control signal is in thefirst direction signal state or the second direction signal state,applying a further gear selection method.
 4. A method as claimed inclaim 3 wherein the further gear selection method comprises: determiningif a direction shift has been requested by the vehicle operator to movethe vehicle from the first direction to the second direction when thetransmission is in an initial first direction gear; and, if so,determining an updated current transmission output speed; comparing theupdated current transmission output speed with a predetermined directionshift threshold transmission output speed; and if the updated currenttransmission output speed is less than or equal to the predetermineddirection shift threshold transmission output speed, causing thetransmission to execute a direction shift from the initial firstdirection gear to a further selected second direction gear, wherein thefurther selected second direction gear corresponds to the initial firstdirection gear or a next highest second direction gear if there is nosecond direction gear which corresponds to the initial first directiongear, and if the updated current transmission output speed is greaterthan the predetermined direction shift threshold transmission outputspeed, inhibiting the direction shift until the updated currenttransmission output speed slows to less than or equal to thepredetermined direction shift threshold transmission output speed. 5.The method as claimed in claim 4 wherein: if the updated currenttransmission output speed is greater that the predetermined directionshift threshold transmission output speed, the transmission is caused toexecute one or more downshifts from the initial first direction gear toa secondary first direction gear which is the lowest gear which has apredetermined downshift inhibit threshold which is greater than theupdated current transmission output speed, each downshift being to thenext highest first direction gear sequentially, and when the updatedcurrent transmission output speed slows to less than or equal to thepredetermined direction shift threshold transmission output speed, andif the direction shift request is still active, the transmission iscaused to execute a direction shift from the secondary first directiongear to a further selected secondary second direction gear, wherein thefurther selected secondary second direction gear corresponds to thesecondary first direction gear or a next highest second direction gearif there is no second direction gear which corresponds to the secondaryfirst direction gear.
 6. The method as claimed in claim 4 wherein: ifthe initial first direction gear is the lowest gear which has apredetermined downshift inhibit threshold which is greater than theupdated current transmission output speed, the initial first directiongear is maintained, and when the updated current transmission outputspeed slows to less than or equal to the predetermined direction shiftthreshold transmission output speed, and if the direction shift requestis still active, the transmission is caused to execute a direction shiftfrom the initial first direction gear to the further selected seconddirection gear.
 7. The method as claimed in claim 1, comprising thefurther step of executing an engine speed reduction signal to reduce aspeed of the power unit.
 8. A method as claimed in claim 1 wherein thedirection detection threshold corresponds to a transmission output speedabove which machine movement is capable of being detected.
 9. A controlsystem for controlling gear selection in a transmission of a vehicle,said vehicle having a power unit and an indirect drive automatictransmission, said transmission having a plurality of first directiongears configured to move the vehicle in a first direction and aplurality of second direction gears configured to move the vehicle in asecond direction which is opposite to the first direction, said controlsystem configured to; evaluate a direction control signal from one ormore input devices controlled by an operator of the vehicle; anddetermine a machine motion direction parameter according to a parametersetting method, in which: when the transmission output speed is below adirection detection threshold, the machine motion direction parameter isset to null; and when the transmission output speed increases to orabove the direction detection threshold, the machine motion directionparameter corresponds to the first direction if a gear of the pluralityof first direction gears is currently engaged or to the second directionif a gear of the plurality of second direction gears is currentlyengaged; and wherein the machine motion direction parameter remainsfixed until the transmission output speed passes below the directiondetection threshold; i) said control system being further configured todetect a change in the direction control signal from a neutral signalstate to a first direction signal state or a second direction signalstate; ii) determine a current transmission output speed; iii) comparethe current transmission output speed with a predetermined neutral shiftthreshold transmission output speed; and either iv a) if the currenttransmission output speed is less than or equal to the predeterminedneutral shift threshold transmission output speed, cause thetransmission to select a gear from the plurality of first directiongears if the direction control signal was changed to the first directionsignal state or to select a gear from the plurality of second directiongears if the direction control signal was changed to the seconddirection signal state; or iv b) if the current transmission outputspeed is greater than the predetermined neutral shift thresholdtransmission output speed, cause the transmission to select a gear fromthe plurality of first direction gears if the machine motion directionparameter indicates that the vehicle is moving in the first direction orto select a gear from the plurality of second direction gears if themachine motion direction parameter indicates that the vehicle is movingin the second direction.
 10. A control system as claimed in claim 9wherein each gear of the plurality of first direction gears or theplurality of second direction gears has a gear selection thresholdtransmission output speed; and wherein the gear selected from theplurality of first direction gears and the plurality of second directiongears is selected by comparison of the current transmission output speedwith the gear selection threshold transmission output speeds.
 11. Acontrol system as claimed in claim 9 further configured to detect anupdated direction control signal after step iv a) or iv b) and either:if the updated direction control signal is in the neutral signal state,causing the transmission to be placed in a neutral condition; or if theupdated direction control signal is in the first direction signal stateor the second direction signal state, apply a further gear selectionmethod.
 12. A control system as claimed in claim 11, wherein during thefurther gear selection method, the control system is configured to:evaluate direction control signals to determine if a direction shiftrequest has been made by the vehicle operator to move the vehicle fromthe first to the second direction when the transmission is in an initialfirst direction gear; and, if so, determine an updated currenttransmission output speed; compare the updated current transmissionoutput speed with a predetermined direction shift threshold transmissionoutput speed; and if the updated current transmission output speed isless than or equal to the predetermined direction shift thresholdtransmission output speed, generate a transmission direction shiftsignal to cause the transmission to execute a direction shift from theinitial first direction gear to a further selected second directiongear, wherein the further selected second direction gear corresponds tothe initial first direction gear or a next highest second direction gearif there is no second direction gear which corresponds to the initialfirst direction gear, and if the updated current transmission outputspeed is greater than the predetermined direction shift thresholdtransmission output speed, inhibit the direction shift until the updatedcurrent transmission output speed slows to less than or equal to thepredetermined direction shift threshold transmission output speed. 13.The control system as claimed in claim 12, wherein: if the updatedcurrent transmission output speed is greater that the predetermineddirection shift threshold transmission output speed, the control systemis further configured to generate a downshift signal to cause thetransmission to execute one or more downshifts from the initial firstdirection gear to a secondary first direction gear which is the lowestgear which has a predetermined downshift inhibit threshold which isgreater than the updated current transmission output speed, eachdownshift being to the next highest first direction gear sequentially,and when the updated current transmission output speed slows to lessthan or equal to the predetermined direction shift thresholdtransmission output speed, and if the direction shift request is stillactive, to generate a direction shift signal which causes thetransmission to execute a direction shift from the secondary firstdirection gear to a further selected secondary second direction gear,wherein the further selected secondary second direction gear correspondsto the secondary first direction gear or a next highest second directiongear if there is no second direction gear which corresponds to thesecondary first direction gear.
 14. The control system as claimed inclaim 12, wherein: if the initial first direction gear is the lowestgear which has a predetermined downshift inhibit threshold which isgreater than the updated current transmission output speed, the controlsystem is configured to maintain the initial first direction gear, andwhen the updated current transmission output speed slows to less than orequal to the predetermined direction shift threshold transmission outputspeed, and if the direction shift request is still active, generate adirection shift signal which causes the transmission to execute adirection shift from the initial first direction gear to the furtherselected second direction gear.
 15. The control system as claimed inclaim 12, wherein the control system is configured to generate an enginespeed reduction signal.
 16. The control system as claimed in claim 9wherein the direction detection threshold corresponds to a transmissionoutput speed above which machine movement is capable of being detected.17. A vehicle comprising: a power unit; an indirect drive automatictransmission, said transmission having a plurality of first directiongears configured to move the vehicle in a first direction and aplurality of second direction gears configured to move the vehicle in asecond direction which is opposite to the first direction; an operatoractuated input direction control configured to generate directioncontrol signals; at least one transmission output speed sensorconfigured to measure current speed of the transmission output andgenerate a transmission output speed signal; and the control system asclaimed in claim 9 operatively connected to the power unit,transmission, input direction control, and at least one transmissionoutput speed sensor.